FIELD OF THE INVENTION
The present invention relates to a boring tool for producing back tapers or undercuts in holes, especially in preformed holes. The boring tool has a cutting element which is provided on one end of a driving shaft, the other end of which is adapted to be connected to a turning drive. The driving shaft, at least in the vicinity of the cutting element, can be deflected at substantially right angles to the axis thereof.
With such a boring tool, preformed, cylindrical holes are provided with undercuts for positive anchoring of mounting elements, such as expanding dowels. The driving shaft is resiliently bendable spring steel and, via a fastening cone, is clamped into the receiving means of a drill which rotatably drives the driving shaft. To produce the undercut, the driving shaft is bent out of the axis of the cylindrical bore by the drill during the drilling process, and at the same time is pivoted about the mouth of the hole in the manner of a stirring movement. In so doing, the driving shaft is resiliently bent, as a result of which the cutting element drills the undercut in the hole. However, with the heretofore known boring tool of this general type, no clean undercuts can be produced in the hole because the entire drill must be manually moved in a circle in order to produce the undercut. With this heretofore known device, the driving shaft is supported against the edge of the hole during the circular movement, as a result of which, especially when the hole is in soft material, the driving shaft can break out, whereupon a true running is no longer assured.
An object of the present invention is to improve a boring tool of the aforementioned general type in such a way that the undercut in the preformed hole can be precisely produced without a circular movement of the turning device, and can be produced independent of the latter even in soft material.